US Secretary of State Condoleezza Rice asked Hill to go to Asia to find out why North Korea has begun reversing the disarmament process and consult with partners in Seoul, Beijing and Tokyo about how to revive the talks.

"The secretary obviously believes it's important for Chris to go out to the region, particularly to go to Pyongyang, to get a sense on the ground as to what's going on," State Department deputy spokesman Robert Wood told reporters.

Hill, who will be accompanied by the State Department's Korea office director Sung Kim, will also "talk with North Korean officials about why they've taken the steps they've taken," Wood added.

Hill, the assistant secretary for East Asian and Pacific affairs, will also try to encourage North Korea to agree to measures allowing experts to verify an accounting of its nuclear programs submitted in June.

North Korea should not find verification to be an "onerous task," Wood said.

"It's a standard... verification package that's been done in other cases in the international community," he added.

Hill was to leave later Monday for Tuesday talks in Seoul with South Korean counterpart Kim Sook, Wood said. He will then travel to Pyongyang, though the exact date was not yet available.

He will later visit Beijing and Tokyo, he added.

"He is going to meet with his counterparts in other capitals in the region to talk about how we can get the North back on the path to what it's committed to doing," Wood said.

Hill will be "in the region looking for ways to work with our allies to bring North Korea into compliance with its obligations," the deputy spokesman said.

Wood signal mounting alarm about developments.

"We're very concerned about some of the reversal of disablement activities that the North has been engaged in," Wood said. "We want to get the process back on track."

The six-nation deal appears close to collapse after the North announced moves to restart its plutonium reprocessing plant and barred UN nuclear inspectors from the building at the Yongbyon complex.

South Korea's Foreign Minister Yu Myung-Hwan said Friday the hard-won agreement "may be going back to square one." The pact groups the two Koreas, the US, Russia, China and Japan.

The North shut down Yongbyon in July 2007 and began disabling the plants in November that year. In return it was to receive one million tons of fuel oil or equivalent energy aid, and the US was to remove it from a terrorism blacklist.

However Washington refuses to delist the North until the communist state accepts inspection procedures to verify a nuclear inventory it handed over in June.

The North says verification is not part of this stage of the six-nation deal and accuses the US of violating its dignity by seeking "house searches" as in Iraq.

The North tested an atomic weapon in October 2006 and is estimated to have produced enough plutonium at Yongbyon to make around six more bombs.

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